JP2023077621A - Laser machined positive electrode manufacturing method - Google Patents

Abstract

To provide a positive electrode manufacturing method in which burr generation at a positive electrode current collector is reduced when a positive electrode current collector and protective layer are laser processed and which is suitable for mass production.SOLUTION: A laser machined positive electrode manufacturing method includes the steps of: preparing a positive electrode which includes a positive electrode current collector, a positive active material layer provided on the positive electrode current collector, and a protective layer provided on the positive electrode current collector and adjoining to the positive active material layer; and cutting a portion of the protective layer with a laser. The output power of the laser is between 950 W and 1150 W. The protective layer contains ceramic particles and a carbon-based conductive material with an average particle size of 0.75 μm to 3 μm.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for manufacturing a laser-machined positive electrode.

In recent years, secondary batteries such as lithium-ion secondary batteries have been used in portable power sources such as personal computers and mobile terminals, and power sources for driving vehicles such as electric vehicles (BEV), hybrid vehicles (HEV), and plug-in hybrid vehicles (PHEV). is preferably used for

A positive electrode used in a secondary battery such as a lithium ion secondary battery generally has a configuration in which a positive electrode active material layer is provided on a positive electrode current collector. Further, the positive electrode generally has a portion where the positive electrode current collector is exposed without the positive electrode active material layer being provided for the purpose of current collection. A technique is known in which a protective layer is provided at the boundary between the exposed portion of the positive electrode current collector and the positive electrode active material layer (see, for example, Patent Documents 1 and 2). In such a positive electrode, in order to form a current collecting tab, the exposed portion of the positive electrode current collector and the protective layer are cut with a laser (see, for example, Patent Document 1). Further, Patent Literature 2 describes adding a carbon-based conductive material to the protective layer in order to improve current collection.

WO2017/204184 Japanese Patent Application Laid-Open No. 2016-12700

When a positive electrode having a protective layer is laser-cut, there is a phenomenon that the positive electrode current collector melted by the laser protrudes and burrs are generated. As a result of intensive studies conducted by the present inventors, the inventors have found the following. When the above-described laser cutting process is performed on a positive electrode whose protective layer does not contain a carbon-based conductive material, burrs may not occur on the positive electrode current collector, and long burrs may occur on the positive electrode current collector. Therefore, in this case, the generation of burrs is unstable, and it is not suitable for mass production of positive electrodes. When the above-described laser cutting process is performed on a positive electrode whose protective layer contains a carbon-based conductive material, burrs formed on the positive electrode current collector become long in a region where the laser output is high. For the mass production of positive electrodes, it is preferable that the laser output is somewhat high, so this case is also not suitable for mass production of positive electrodes.

In view of the above circumstances, it is an object of the present invention to provide a method for manufacturing a positive electrode in which burrs are reduced in the positive electrode current collector when the positive electrode current collector and the protective layer are laser-processed, and which is suitable for mass production. With the goal.

A method for manufacturing a laser-processed positive electrode disclosed herein includes: a positive electrode current collector; a positive electrode active material layer provided on the positive electrode current collector; The method includes providing a positive electrode comprising a protective layer adjacent to an active material layer, and laser cutting a portion of the protective layer. The power of the laser is 950W or more and 1150W or less. The protective layer contains ceramic particles and a carbon-based conductive material having an average particle size of 0.75 μm or more and 3 μm or less.

According to such a configuration, it is possible to provide a method for manufacturing a positive electrode in which burrs are reduced in the positive electrode current collector when the positive electrode current collector and the protective layer are laser-processed, and which is suitable for mass production. can.

In a preferred embodiment of the laser-processed positive electrode manufacturing method disclosed herein, the carbon-based conductive material is carbon black.

In another preferred aspect of the method for producing a laser-processed positive electrode disclosed herein, the content of the carbon-based conductive material in the protective layer is 0.1% by mass or more and 5.0% by mass or less.

In still another preferred aspect of the method for producing a laser-processed positive electrode disclosed herein, the output of the laser is 950 W or more and 1050 W or less.

It is a flow chart which shows each process of the manufacturing method concerning one embodiment of the present invention. 1 is a schematic cross-sectional view of an example of a positive electrode prepared in one embodiment of the present invention; FIG. 1 is a schematic diagram of an example of a positive electrode prepared in one embodiment of the present invention, viewed from a direction perpendicular to the main surface; FIG. 1 is a cross-sectional view schematically showing the configuration of a lithium-ion secondary battery constructed using a positive electrode obtained according to one embodiment of the present invention; FIG. FIG. 5 is a schematic exploded view showing the configuration of the wound electrode assembly of the lithium ion secondary battery of FIG. 4; 4 is a graph showing burr length ratios with respect to laser power in Test Examples 1 and 2. FIG.

Hereinafter, embodiments according to the present invention will be described with reference to the drawings. Matters not mentioned in this specification but necessary for the implementation of the present invention can be grasped as design matters by those skilled in the art based on the prior art in the relevant field. The present invention can be implemented based on the contents disclosed in this specification and common general technical knowledge in the field. Moreover, in the following drawings, members and parts having the same function are denoted by the same reference numerals. Also, the dimensional relationships (length, width, thickness, etc.) in each drawing do not reflect the actual dimensional relationships.

In this specification, the term “secondary battery” refers to an electricity storage device that can be repeatedly charged and discharged, and is a term that includes so-called storage batteries and electricity storage elements such as electric double layer capacitors. In this specification, the term “lithium ion secondary battery” refers to a secondary battery that utilizes lithium ions as a charge carrier and is charged/discharged by the transfer of charge associated with the lithium ions between the positive and negative electrodes.

Hereinafter, as an example, an embodiment in which the laser-processed positive electrode obtained by the manufacturing method disclosed herein is a positive electrode for a lithium ion secondary battery will be specifically described with reference to the drawings.

As shown in FIG. 1, the method for manufacturing a laser-processed positive electrode according to the present embodiment comprises: a positive electrode current collector; a positive electrode active material layer provided on the positive electrode current collector; and a protective layer adjacent to the positive electrode active material layer (hereinafter also referred to as “positive electrode preparation step”) S101; and a step of laser cutting a part of the protective layer (hereinafter , S102 (also referred to as a "laser cutting step"). Here, the output of the laser used for cutting is 950 W or more and 1150 W or less. The protective layer contains ceramic particles and a carbon-based conductive material having an average particle size of 0.75 μm or more and 3 μm or less.

First, the positive electrode preparation step S101 will be described. 2 and 3 show an example of the positive electrode prepared in step S101. FIG. 2 is a cross-sectional view along the width direction and thickness direction of the positive electrode. FIG. 3 is a schematic diagram of the positive electrode viewed from the direction perpendicular to the main surface.

The positive electrode 50 in the illustrated example is configured as an elongated positive electrode sheet, and only a portion of it is illustrated in FIG. 3 . However, the positive electrode does not have to be elongated. As shown in FIGS. 2 and 3 , the positive electrode 50 includes a positive electrode current collector 52 and a positive electrode active material layer 54 formed on the positive electrode current collector 52 . In the illustrated example, the positive electrode active material layer 54 is provided on both surfaces of the positive electrode current collector 52 . However, the positive electrode active material layer 54 may be provided only on one side of the positive electrode current collector 52 .

The main surface of the positive electrode current collector 52 has a portion (positive electrode current collector exposed portion) 52a where the positive electrode current collector 52 is exposed without the positive electrode active material layer 54 being formed. In the illustrated example, the positive electrode current collector exposed portion 52a is provided at one end portion of the positive electrode 50 in the width direction. However, the positive electrode current collector exposed portion 52 a may be provided at the longitudinal end portion of the positive electrode 50 . Also, the positive electrode current collector exposed portion 52 a may be provided at two or more ends of the positive electrode 50 .

The positive electrode 50 has a protective layer 56 . In the illustrated example, the protective layers 56 are provided on both sides of the positive electrode current collector 52 . However, the protective layer 56 may be provided only on one side of the positive electrode current collector 52 .

The protective layer 56 is adjacent to the positive electrode active material layer 54 and positioned between the positive electrode active material layer 54 and the positive electrode current collector exposed portion 52 a in the surface direction of the positive electrode sheet 50 . In other words, the protective layer 56 is located at the boundary between the positive electrode active material layer 54 and the positive electrode current collector exposed portion 52a. By providing the protective layer 56 at this position, a short circuit between the positive electrode 50 and the negative electrode 60 can be highly suppressed.

The positive electrode current collector 52 is generally a highly conductive metal member. As the positive electrode current collector 52, for example, a sheet-like member such as metal foil, metal mesh, or punching metal can be used. The positive electrode current collector 52 is preferably a member made of aluminum or an aluminum alloy, more preferably an aluminum foil.

The dimensions of the positive electrode current collector 52 are not particularly limited, and may be appropriately determined according to the battery design. When an aluminum foil is used as the positive electrode current collector 52, its thickness is not particularly limited, but is, for example, 5 μm or more and 35 μm or less, preferably 7 μm or more and 20 μm or less.

The positive electrode active material layer 54 contains a positive electrode active material. As the positive electrode active material, a known positive electrode active material used for lithium ion secondary batteries may be used. Specifically, for example, a lithium composite oxide, a lithium transition metal phosphate compound, or the like can be used as the positive electrode active material. The crystal structure of the positive electrode active material is not particularly limited, and may be a layered structure, a spinel structure, an olivine structure, or the like.

As the lithium composite oxide, a lithium transition metal composite oxide containing at least one of Ni, Co, and Mn as a transition metal element is preferable. Composite oxides, lithium manganese composite oxides, lithium nickel manganese composite oxides, lithium nickel cobalt manganese composite oxides, lithium nickel cobalt aluminum composite oxides, lithium iron nickel manganese composite oxides, and the like. These positive electrode active materials may be used singly or in combination of two or more. A lithium-nickel-cobalt-manganese-based composite oxide is preferable as the positive electrode active material.

In this specification, the term "lithium-nickel-cobalt-manganese-based composite oxide" refers to an oxide containing Li, Ni, Co, Mn, and O as constituent elements, and one or more of these oxides. It is a term that also includes oxides containing such elements. Examples of such additive elements include transition metal elements such as Mg, Ca, Al, Ti, V, Cr, Y, Zr, Nb, Mo, Hf, Ta, W, Na, Fe, Zn and Sn, and typical A metal element etc. are mentioned. Also, the additive elements may be metalloid elements such as B, C, Si and P, and nonmetal elements such as S, F, Cl, Br and I. This is because the above-described lithium-nickel-based composite oxide, lithium-cobalt-based composite oxide, lithium-manganese-based composite oxide, lithium-nickel-manganese-based composite oxide, lithium-nickel-cobalt-aluminum-based composite oxide, and lithium-iron-nickel-manganese-based composite The same applies to oxides and the like.

Examples of lithium transition metal phosphate compounds include lithium iron phosphate (LiFePO ₄ ), lithium manganese phosphate (LiMnPO ₄ ), lithium manganese iron phosphate, and the like.

The above positive electrode active materials can be used singly or in combination of two or more.

The average particle size of the positive electrode active material is not particularly limited, but is, for example, 0.05 μm or more and 25 μm or less, preferably 1 μm or more and 20 μm or less, more preferably 3 μm or more and 15 μm or less. In this specification, the term "average particle size" refers to the median size (D50). It means the particle size corresponding to the volume %. Therefore, the average particle diameter (D50) can be determined using a known laser diffraction/scattering particle size distribution analyzer or the like.

The positive electrode active material layer 54 may contain components other than the positive electrode active material, such as trilithium phosphate, a conductive material, a binder, and the like. Carbon black such as acetylene black (AB) and other carbon materials (eg, graphite) can be suitably used as the conductive material. As the binder, for example, polyvinylidene fluoride (PVDF) or the like can be used.

The content of the positive electrode active material in the positive electrode active material layer 54 (that is, the content of the positive electrode active material with respect to the total mass of the positive electrode active material layer 54) is not particularly limited, but is preferably 70% by mass or more, more preferably 80% by mass. It is 97% by mass or more, more preferably 85% by mass or more and 96% by mass or less. The content of trilithium phosphate in the positive electrode active material layer 54 is not particularly limited, but is preferably 1% by mass or more and 15% by mass or less, more preferably 2% by mass or more and 12% by mass or less. The content of the conductive material in the positive electrode active material layer 54 is not particularly limited, but is preferably 1% by mass or more and 15% by mass or less, more preferably 3% by mass or more and 13% by mass or less. The content of the binder in the positive electrode active material layer 54 is not particularly limited, but is preferably 1% by mass or more and 15% by mass or less, more preferably 1.5% by mass or more and 10% by mass or less.

Although the thickness of the positive electrode active material layer 54 is not particularly limited, it is, for example, 10 μm or more and 300 μm or less, preferably 20 μm or more and 200 μm or less.

The protective layer 56 contains ceramic particles and a carbon-based conductive material. Since the protective layer 56 contains the carbon-based conductive material, the current collecting property of the positive electrode 50 is enhanced. The protective layer 56 may further contain a binder.

Examples of ceramic particles contained in the protective layer ₅₆ include alumina ( _Al2O3 ), silica ( _SiO2 ), titania ( _TiO2 ), zirconia ( _ZrO2 ), magnesia (MgO), ceria ( _CeO2 ), Particles of oxide ceramics such as zinc oxide (ZnO); particles of nitride ceramics such as silicon nitride, titanium nitride and boron nitride; particles of hydroxides such as calcium hydroxide, magnesium hydroxide and aluminum hydroxide; Particles of clay minerals such as mica, talc, boehmite, zeolite, apatite, and kaolin are included. Among them, alumina particles and boehmite particles are preferably used. Alumina and boehmite have high melting points and excellent heat resistance. Alumina and boehmite also have a relatively high Mohs hardness and excellent mechanical strength and durability. Furthermore, since alumina and boehmite are relatively inexpensive, raw material costs can be suppressed.

The shape of the ceramic particles is not particularly limited, and may be spherical or non-spherical. The average particle diameter (D50) of the ceramic particles is not particularly limited, and is, for example, 0.01 μm or more and 10 μm or less, preferably 0.1 μm or more and 5 μm or less, more preferably 0.2 μm or more and 2.0 μm or less. .

The content of the ceramic particles in the protective layer 56 is not particularly limited, but is, for example, 70% by mass or more, preferably 75% by mass or more, and more preferably 85% by mass or more.

Examples of the carbon-based conductive material contained in the protective layer 56 include carbon black such as acetylene black, furnace black, channel black, thermal black, and ketjen black, and graphite. Among them, carbon black is preferable because it has a high performance of absorbing heat during laser processing (that is, laser cutting) and can suppress peeling between the protective layer 56 and the positive electrode current collector 52 . Among carbon blacks, acetylene black is more preferable.

In the present embodiment, the average particle size (median size D50) of the carbon-based conductive material is 0.75 μm or more and 3 μm or less. From the viewpoint of a higher burr reduction effect, the average particle size of the carbon-based conductive material is preferably 1.0 μm or more, more preferably 1.1 μm or more. From the viewpoint of a higher burr reduction effect, the average particle size of the carbon-based conductive material is preferably 2.5 μm or less, more preferably 2.0 μm or less, and even more preferably 1.5 μm or less. The method for measuring the average particle size of the carbon-based conductive material is as described above.

The content of the carbon-based conductive material in the protective layer 56 is not particularly limited as long as the effects of the present invention can be obtained, and is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, More preferably, it is 0.3% by mass or more. The content of the carbon-based conductive material in the protective layer 56 is preferably 5.0% by mass or less, more preferably 4.0% by mass or less, still more preferably 3.0% by mass or less, and further It is more preferably 2.5% by mass or less, particularly preferably 1.0% by mass or less, and most preferably 0.6% by mass or less.

Examples of binders contained in the protective layer 56 include acrylic binders, styrene-butadiene rubber (SBR), polyolefin binders, and fluorine-based binders such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE). Polymers can also be used.

The content of the binder in the protective layer 56 is not particularly limited, but is, for example, 1% by mass to 25% by mass, preferably 3% by mass to 20% by mass, and more preferably 3% by mass It is more than 10 mass % or less.

Although the thickness of the protective layer 56 is not particularly limited, it is preferably 3 μm or more and equal to or less than the thickness of the positive electrode active material layer 54 . More preferably, the thickness of the protective layer 56 is 5 μm or more and 50 μm or less.

The positive electrode 50 may further include layers other than the positive electrode active material layer 54 and the protective layer 56 within a range that does not impair the effects of the present invention.

Such a positive electrode 50 can be produced, for example, as follows. That is, the positive electrode preparation step S101 can be performed, for example, as follows.

First, a positive electrode active material layer-forming slurry (or paste) containing a positive electrode active material, a first solvent (first dispersant), and, if necessary, a conductive material, a binder, and the like is prepared. As the first solvent, a solvent used in a conventional positive electrode active material layer forming slurry can be used. Also, prepare a slurry (or paste) for forming a protective layer containing ceramic particles, a carbon-based conductive material having a predetermined average particle size, a second solvent (second dispersant), and, if necessary, a binder and the like. . As the second solvent, a solvent used in a conventional protective layer forming slurry can be used.

Next, the slurry for forming the positive electrode active material layer and the slurry for forming the protective layer are applied to one side or both sides of the positive electrode current collector 52 . At this time, the slurry for forming the positive electrode active material layer and the slurry for forming the protective layer may be applied such that at least one end of the positive electrode current collector 52 is exposed. The slurry for forming the positive electrode active material layer and the slurry for forming the protective layer are applied so as to be adjacent to each other. Such coating can be performed by a known method (for example, a method of sequentially or simultaneously coating the slurry for forming the positive electrode active material layer and the slurry for forming the protective layer using a die coater).

These coated slurries are then dried according to known methods. Specifically, for example, the solvent is removed from the positive electrode current collector coated with these slurries using a drying device such as a drying furnace. Thereby, the positive electrode active material layer 54 and the protective layer 56 can be formed. For the purpose of adjusting the density and the like of the positive electrode active material layer 54, the formed positive electrode active material layer 54 may be subjected to press treatment. Thus, the positive electrode 50 can be obtained.

Next, the laser cutting step S102 will be described. In step S102, a portion of the protective layer 56 is cut using a laser. Typically, in step S102, a part of the positive electrode current collector exposed part 52a and a part of the protective layer 56 are cut to form a current collecting tab. The shape of the current collecting tab is not particularly limited, and examples thereof include those shown in FIG. Alternatively, in order to cut the positive electrode 50 into a predetermined size, laser cutting may be performed along the width direction of the positive electrode 50, and a part of the protective layer 56 may be cut at this time. Since the distance to cut the protective layer 56 is long and the effect of the present invention becomes more remarkable, it is preferable to form a current collecting tab in the step S102.

For laser cutting, a known laser cutting apparatus used for laser cutting a positive electrode having a protective layer containing ceramic particles can be used. The laser cutting device is typically a cutting device with a fiber laser. Therefore, the laser used for cutting is typically a fiber laser.

In this embodiment, the output of the laser used for cutting is in the range of 950 W or more and 1150 W or less. The protective layer 56 contains a carbon-based conductive material having an average particle size of 0.75 μm or more and 3 μm or less, and at least a part of the protective layer 56 is cut with a laser at an output within the range of 950 W or more and 1150 W or less, thereby forming a positive electrode. The generation of burrs on the current collector can be significantly reduced. Moreover, since the output of the laser is 950 W or more, the manufacturing method according to this embodiment is suitable for mass production. Moreover, when the output of the laser exceeds 1150 W, the cutting quality deteriorates. From the viewpoint of further reducing the occurrence of burrs, the laser output is preferably 950 W or more and 1050 W or less, more preferably 975 W or more and 1025 W or less.

Although the scanning speed of the laser is not particularly limited, it is preferably 1000 mm/s or more and 12000 mm/s or less, more preferably 2000 mm/s or more and 10000 mm/s or less, and still more preferably 4000 mm/s or more and 8000 mm/s or less. be.

As described above, the laser-processed positive electrode 50 can be obtained. The laser-processed positive electrode 50 can be used as a positive electrode of a secondary battery (particularly a lithium ion secondary battery) according to a known method. Hereinafter, as an example of a secondary battery using the positive electrode 50 obtained by the manufacturing method according to the present embodiment, a configuration example of a lithium ion secondary battery using the positive electrode 50 will be described with reference to the drawings.

The lithium ion secondary battery 100 shown in FIG. 4 is a closed type constructed by housing a flat wound electrode body 20 and a non-aqueous electrolyte 80 in a flat rectangular battery case (that is, an outer container) 30. Battery. The battery case 30 is provided with a positive terminal 42 and a negative terminal 44 for external connection, and a thin safety valve 36 set to release the internal pressure when the internal pressure of the battery case 30 rises above a predetermined level. ing. Further, the battery case 30 is provided with an injection port (not shown) for injecting the non-aqueous electrolyte 80 . The positive terminal 42 is electrically connected to the positive collector plate 42a. The negative terminal 44 is electrically connected to the negative collector plate 44a. As the material of the battery case 30, for example, a metal material such as aluminum that is lightweight and has good thermal conductivity is used. Note that FIG. 4 does not accurately represent the amount of non-aqueous electrolyte 80 .

As shown in FIGS. 4 and 5, the wound electrode body 20 is formed by stacking a positive electrode sheet 50 and a negative electrode sheet 60 with two elongated separator sheets 70 interposed therebetween and winding them in the longitudinal direction. morphology. The positive electrode sheet 50 has a configuration in which a positive electrode active material layer 54 is formed along the longitudinal direction on one side or both sides (here, both sides) of a long positive electrode current collector 52 . The negative electrode sheet 60 has a configuration in which a negative electrode active material layer 64 is formed along the longitudinal direction on one side or both sides (here, both sides) of a long negative electrode current collector 62 .

A positive electrode obtained by the above-described manufacturing method is used for the positive electrode sheet 50 . Specifically, as shown in FIG. 4, the positive electrode 50 has a portion (positive electrode current collector exposed portion) 52a where the positive electrode current collector 52 is exposed without the positive electrode active material layer 54 being formed. A protective layer 56 is provided at the boundary between the positive electrode active material layer 54 and the positive electrode current collector exposed portion 52a. The positive electrode current collector exposed portion 52a and the protective layer 56 are laser-cut to form the positive electrode current collector exposed portion 52a as a current collecting tab.

As shown in FIGS. 4 and 5, the negative electrode 60 has a portion (negative electrode current collector exposed portion) 62a in which the negative electrode current collector 62 is exposed without the negative electrode active material layer 64 formed thereon. The exposed portion 62a is configured as a current collecting tab.

The positive electrode current collector exposed portion 52a and the negative electrode current collector exposed portion 62a, which are in the form of current collecting tabs, extend in the direction of the winding axis WL of the wound electrode body 20 (that is, the sheet width direction orthogonal to the longitudinal direction). It is formed so as to protrude outward from both ends. The positive electrode current collector exposed portion 52a and the negative electrode current collector exposed portion 62a are respectively bundled and joined to the positive electrode current collector plate 42a and the negative electrode current collector plate 44a.

Examples of the negative electrode current collector 62 forming the negative electrode sheet 60 include copper foil. The negative electrode active material layer 64 contains a negative electrode active material. Carbon materials such as graphite, hard carbon, and soft carbon can be used as the negative electrode active material. The negative electrode active material layer 64 may further contain binders, thickeners, and the like. As the binder, for example, styrene-butadiene rubber (SBR) or the like can be used. As a thickening agent, for example, carboxymethyl cellulose (CMC) or the like can be used.

As the separator 70, various microporous sheets similar to those conventionally used in lithium ion secondary batteries can be used. A porous resin sheet is mentioned. Such a microporous resin sheet may have a single-layer structure or a multi-layer structure of two or more layers (for example, a three-layer structure in which PP layers are laminated on both sides of a PE layer). The separator 70 may comprise a heat resistant layer (HRL).

Non-aqueous electrolyte 80 typically contains a non-aqueous solvent and an electrolyte salt (in other words, a supporting salt). As the non-aqueous solvent, organic solvents such as various carbonates, ethers, esters, nitriles, sulfones, lactones, etc., which are used in electrolytes of general lithium ion secondary batteries, can be used without particular limitation. can. Among them, carbonates are preferred.

As the electrolyte salt, for example, lithium salts such as LiPF ₆ , LiBF ₄ and lithium bis(fluorosulfonyl)imide (LiFSI) can be used, among which LiPF ₆ is preferred. The concentration of the electrolyte salt is not particularly limited, but is preferably 0.7 mol/L or more and 1.3 mol/L or less.

The non-aqueous electrolyte 80 may include components other than the components described above, such as oxalato complexes, film-forming agents such as vinylene carbonate (VC), biphenyl (BP), and cyclohexylbenzene, as long as the effects of the present invention are not significantly impaired. Gas generating agents such as (CHB); thickeners; and other various additives may be included.

The lithium ion secondary battery 100 can be used for various purposes. Suitable applications include drive power supplies mounted in vehicles such as electric vehicles (BEV), hybrid vehicles (HEV), and plug-in hybrid vehicles (PHEV). Moreover, the lithium ion secondary battery 100 can be used as a storage battery such as a small power storage device. The lithium ion secondary battery 100 can also be used typically in the form of an assembled battery in which a plurality of batteries are connected in series and/or in parallel.

As an example, the prismatic lithium ion secondary battery 100 including the flattened wound electrode body 20 has been described. However, the lithium ion secondary battery disclosed herein may be configured as a lithium ion secondary battery including a laminated electrode body (that is, an electrode body in which a plurality of positive electrodes and a plurality of negative electrodes are alternately laminated). can also The nonaqueous electrolyte secondary battery disclosed herein can also be configured as a cylindrical lithium ion secondary battery, a laminate case type lithium ion secondary battery, a coin type lithium ion secondary battery, or the like.

Moreover, according to a known method, a non-aqueous electrolyte secondary battery other than a lithium ion secondary battery can also be constructed using the positive electrode described above. Furthermore, according to a known method, a solid electrolyte can be used instead of the non-aqueous electrolyte 80 to construct an all-solid secondary battery (in particular, an all-solid lithium ion secondary battery).

Test examples relating to the present invention will be described below, but the present invention is not intended to be limited to those shown in such test examples.

[Preparation of test sheets for Test Examples 1 to 3]
Alumina as ceramic particles, polyvinylidene fluoride (PVDF) as a binder, and acetylene black (AB) as a carbon-based conductive material were mixed in N-methylpyrrolidone to prepare a slurry for forming a protective layer. At this time, AB having an average particle size shown in Table 1 was used, and the content of AB with respect to the total solid content of the protective layer forming slurry was set to the value shown in Table 1.

A protective layer forming paste was applied on both sides of a 13 μm thick aluminum foil as a current collector using a bar coater and dried to prepare test sheets of Test Examples 1 to 3. In the manufacturing method described above, since the protective layer and the positive electrode current collector were laser-cut, the positive electrode active material layer was omitted from the test sheet.

[Laser cutting of test sheet]
Using a commercially available laser machine equipped with a fiber laser irradiation unit, the current collector and protective layer of the test sheet prepared above were laser-cut. At this time, the scanning speed was set to 6000 mm/sec, and the laser output was set to the values shown in Table 2.

[Evaluation of burr generation on test sheet]
The length of burrs generated at the laser-cut portion of the test sheet was measured. Assuming that the length of the burr in Test Example 1 at a laser output of 1100 W is 100, the length ratio of other burrs was calculated. Table 2 shows the results.

FIG. 6 shows a graph of the results of Test Example 1 and Test Example 2 in Table 2. In FIG. As a general trend, the higher the laser output, the longer the length of burrs generated on the current collector. As the results in Table 2 and FIG. 6 show, this tendency was observed in Test Example 1. Here, in Test Example 1, when the laser output is 900 W or less, although the burr length is short, the laser output is too small to be suitable for mass production. When the laser output was 1000 W and 1100 W, which are suitable for mass production, the burr length ratios were very large, 71 and 100, respectively.

On the other hand, in Test Example 2, in which the average particle size of acetylene black was reduced, burr generation was reduced compared to Test Example 1, specifically when the laser output was 1000 W and 1100 W, which are suitable for mass production ( See Figure 6). In Test Example 3, the AB content was set to the same level as in Test Example 1, but the generation of burrs was reduced. From this, it can be seen that the average particle size of acetylene black affects the length of burrs generated on the positive electrode current collector. From the above results, it is considered that when the average particle size of acetylene black is 0.75 μm or more and 3 μm or less, the generation of burrs can be significantly reduced.

From the above, it can be seen that the manufacturing method disclosed herein can reduce the generation of burrs when laser processing the positive electrode current collector and the protective layer, and is suitable for mass production.

Although specific examples of the present invention have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

20 Wound electrode assembly 30 Battery case 36 Safety valve 42 Positive electrode terminal 42a Positive electrode current collector 44 Negative electrode terminal 44a Negative electrode current collector 50 Positive electrode sheet (positive electrode)
52 positive electrode current collector 52a positive electrode current collector exposed portion 54 positive electrode active material layer 56 protective layer 60 negative electrode sheet (negative electrode)
62 Negative electrode current collector 62a Negative electrode current collector exposed portion 64 Negative electrode active material layer 70 Separator sheet (separator)
80 nonaqueous electrolyte 100 lithium ion secondary battery

Claims (4)

A positive electrode comprising a positive electrode current collector, a positive electrode active material layer provided on the positive electrode current collector, and a protective layer provided on the positive electrode current collector and adjacent to the positive electrode active material layer is prepared. process and
laser cutting a portion of the protective layer, comprising:
The output of the laser is 950 W or more and 1150 W or less,
The manufacturing method, wherein the protective layer contains ceramic particles and a carbon-based conductive material having an average particle size of 0.75 μm or more and 3 μm or less. The manufacturing method according to claim 1, wherein the carbon-based conductive material is carbon black. The manufacturing method according to claim 1 or 2, wherein the content of the carbon-based conductive material in the protective layer is 0.1% by mass or more and 5.0% by mass or less. The manufacturing method according to any one of claims 1 to 3, wherein the output of said laser is 950 W or more and 1050 W or less.

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